1. Field of the Invention
The present invention relates to a web offset press, and more particularly to a method and an apparatus for replacing a printing plate, which enables a worker to easily replace the printing plate by using a scaffold installed between printing units in a case that the printing plate of a plate cylinder provided in the printing unit in a variable cutoff rotary press where a diameter of the plate cylinder is able to be changed is replaced.
2. Description of the Related Art
A printing section of a web offset press is composed of a plurality of printing units, and in each of the printing units, an upper blanket cylinder and an upper plate cylinder are provided at an upper part of a web, and a lower blanket cylinder and a lower plate cylinder are provided at a lower part of the web while sandwiching the web. A picture on a printing plate wound around the upper plate cylinder is transferred onto an upper surface of the web via the upper blanket cylinder, and a picture on a printing plate wound around the lower plate cylinder is transferred onto a lower surface of the web via the lower blanket cylinder.
Each of the printing units is that for printing a cyan, yellow, magenta, and black, respectively, and by utilizing a color mixture thereof, a color printing is achieved. A scaffold is installed between printing units adjacent to each other at a height of approximately a chest of humans, and a worker performs an exchange of ink, maintenance for a group of various kinds of rollers, and a work for replacing a printing plate while climbing up the scaffold.
As a scaffold device for maintenance and repair, for use in the printing press, for example, a step device installed between printing units in a multicolor press or the like is disclosed in the Unexamined Japanese Patent Application Publication No. 11-198341. Further, in the Unexamined Japanese Patent Application Publication No. 2001-315295, a scaffold device where a step plate is enabled to be raised and lowered by means of a lifting and lowering device such as a pantograph mechanism or the like is disclosed. Furthermore, in the Unexamined Japanese Patent Application Publication No. 2002-29023, a scaffold device, which is movable between a working position and a waiting position for a printing unit, and is disposed at a position where a moving trajectory thereof does not interfere an apparatus for replacing a printing plate is disclosed.
In such a conventional web offset press as described above, the work for replacing a printing plate wound around a plate cylinder is performed in the following procedure, in which one end of the printing plate is removed first, the printing plate is removed while rotating the plate cylinder in one rotation, and finally another end is removed. Next, a new printing plate is attached in a reverse procedure to that of removing the printing plate while rotating the plate cylinder in one rotation.
Although such work for replacing the printing plate is performed by using the scaffold installed between printing units for the upper plate cylinder, specifically, in a case of a variable cutoff rotary press where a diameter of the plate cylinder is able to be changed, since a device for enabling to change the diameter of the plate cylinder or the like is installed, a distance between the scaffold and the upper plate cylinder is large and a place at a height of the upper plate cylinder is located at a position close to an upper surface of the scaffold for a structural reason. Hence, in a case that a worker replaces the printing plate of the upper plate cylinder, the worker has been obliged to perform such work as removing an old printing plate from, and replacing a new printing plate to the plate cylinder located at a place at a height near a level of a foot with an extraordinary difficulty in a labored posture in an unnatural posture while hunkering down and stretching. Therefore, accuracy of attaching the printing plate becomes unstable, and it has been taking much time for replacing the printing plate. However, any of a device or a method for solving such work is not disclosed in the Unexamined Japanese Patent Application Publication Nos. 11-198341, 2001-315295, and 2002-29023.
Even when the scaffold is intended to be disposed at a relatively lower position so that the aforementioned work is improved, the scaffold cannot be disposed at the relatively lower position because a travel path of the web (web path line) is located below the scaffold and thereby it is possible for the scaffold to be brought into contact with the web. Since the web between the printing units is in a process of just after printed by means of the printing unit, the ink on the web has not been dried yet, and therefore elements other than blanket cylinders are avoided to contact the web between each of the printing units. On the other hand, as for the work for replacing the printing plate of the lower plate cylinder, there is no necessity for the worker to ride on the scaffold hung between printing units and the work for replacing the printing plate can be performed in a relatively easy posture on a step provided on a floor surface.